The proposed research is designed to further our understanding of physiological changes which occur in the reproductive systems of aged monkeys. Preliminary evidence from our laboratory indicates that during senescence the reproductive system of the rhesus monkey undergoes very similar changes to those changes reported in humans. Initial studies have been designed to compare the patterns of pituitary gonadotropin and prolactin secretion as well as the gonadal steroid output in senescent and young adult animals. Utilizing these data, studies will be designed to explore possible changes in the sensitivities of the testes, ovaries, uterus, anterior pituitary and hypothalamus of aged animals to specific hormonal stimulation and/or inhibition. These results should help determine if the physiological function of the specific tissue being studied is: 1. the consequence of aging within that tissue per se, 2. due to aging changes in other regulatory tissues, or 3. a general aging effect on all tissues being examined. A minimum of 36 monkeys known to be over 20 years of age is presently available for geriatric studies at the Wisconsin Regional Primate Research Center. In addition, the Primate Laboratory of the Univeristy of Wisconsin Department of Psychology (adjacent to the Primate Center) has 20 monkeys, ages 20-30 years, which may be utilized in temporary descriptive studies or perhaps purchased if more animals are needed. In studies requiring frequent or long-term manipulation, chair-adapted rhesus monkeys with indwelling catheters will be utilized to obtain multiple blood samples for determining hormonal secretory patterns for the infusion of other hormones and/or drugs, and to obtain data on internal and external measurements of body temperature. Methods to be used include double antibody radioimmunoassay of pituitary hormones as well as radioimmunoassay and protein binding techniques for steroid determinations. In vitro incubations will be utilized for steroid metabolism studies in the gonads and uterus. Data logging systems will be employed for obtaining records of body temperature.